The closest known prior art to the present invention is Geller et al U.S. Pat. No. 2,969,452 issued in 1961. That patent shows an electrically heated pan in which the heat is distributed by an oil bath. FIG. 3 of the Geller patent shows that the inner container and the outer container which receive the oil between them are brought to contacting surfaces at the top edge which are welded to form a seal. In practice, while this generally works it does have some disadvantages. In order to form a finished edge the welded area must be ground, which is an extra finishing operation, and grinding will sometimes expose imperfections in the weld which can cause uncontrolled leakage. Geller discloses that his oil cavity is filled at an opening 21 which is sealed by applying the handle to the pan. Such a seal may or may not be effective and may or may not be permanent. It affords no opportunity for pressure relief if needed.